Quaternary ammonium salts carrying two hydrophobic long chain hydrocarbon moieties have found broad use as fabric softener actives. Quaternary ammonium salts of alkanolamines esterified with on average two fatty acid moieties per molecule, commonly referred to as ester quats, have largely replaced earlier alkyl quaternary ammonium compounds because of their biodegradability.
Bis-(2-hydroxyethyl)-dimethylammonium chloride fatty acid diesters, which have found commercial use, are difficult to handle in a pure state, since the solid tends to lump and the melt has high viscosity at low melt temperatures and unsatisfactory stability at higher melt temperatures. Therefore, bis-(2-hydroxyethyl)-dimethylammonium chloride fatty acid diesters are usually shipped as a molten composition containing at least 13% by weight of ethanol or 2-propanol, which has a viscosity at temperatures of 65 to 75° C. that is sufficiently low for pumping. However, such compositions have a low flash point of less than 30° C. and are therefore subject to regulatory restrictions and require additional safety measures in handling.
WO 2007/026314 proposes to replace the flammable solvent of such compositions by 2 to 40% by weight of a diluent chosen from alkyl esters or polyesters, alkyl amides or polyamides, fatty acids, nonionics or combinations thereof and specifically discloses hydrogenated tallow fat, hydrogenated tallow fatty acid, hydrogenated coconut oil, hydrogenated palm stearine, hydrogenated soy oil, ethylene glycol distearate hard soy sucrose ester, cetyl palmitate and pentaerythritol tetracaprylate/tetracaprate as suitable diluents. WO 2007/026314 further proposes to use an additional coupling agent, selected from polyhydric alcohols, partial esters of polyhydric alcohols non-ionic surfactants, in an amount of from 0.1 to 15% by weight. However, the compositions taught by WO 2007/026314 have the disadvantage of a low stability in the molten state with respect to dealkylation of the quaternary ammonium salt, which leads to an increase in the content of free ester amine during transport and handling in a molten state.
Therefore, there is still a need for fabric softener active compositions which have a low melt viscosity and high stability in a molten state and at the same time have a low flammability.